1. Field of the Invention
The present invention relates to the liquid/liquid extraction of gallium values from basic aqueous solutions, and, more especially, from the sodium aluminate liquor emanating from the production of alumina via the Bayer process, utilizing an organic phase which includes a substituted hydroxyquinoline gallium extractant and an organic solvent, wherein, in addition to the gallium values, sodium and aluminum are also transferred into the organic phase.
2. Description of the Prior Art
In the well known Bayer process for the production of aluminum oxide from aluminum ores (bauxites), such ores are decomposed at an elevated temperature and under an increased pressure with caustic solution. Aluminum hydroxide may be precipitated from the sodium aluminate lye, which is then calcined into Al.sub.2 O.sub.3 (alumina).
In this process, the gallium contained in the bauxite is concentrated in the sodium aluminate lye.
Over the course of the extraction of the gallium from this lye, large amounts of sodium, among others, are also extracted. The respective amounts (proportions) vary greatly. They depend, on the one hand, on the composition of the sodium aluminate lye, and, on the other, on the concentration and nature of the substituted hydroxyquinoline, the organic solvent and optional additives.
Typical concentration ratios of the sodium/aluminum/gallium values in the organic phase are about 250/25/1.
Under these conditions, the Bayer process loses caustic, which must be replaced.
In the known processes, in addition to gallium and aluminum, sodium is also stripped by means of acids, which mandates the use of both corrosion resistant apparatus and large amounts of acids.
Processes of this known type are described, for example, in DE-PS 25 30 880, DE-OS 27 43 475 and EP-OS 0 145 659.
In one of these processes, the organic solution charged with the extraction agent is stripped in a first state by means of a weakly concentrated strong acid, wherein the waste material is an acid solution containing sodium and aluminum salts. This solution is separated from the organic phase. Subsequently, in another stage, the organic phase is stripped with a more highly concentrated acid, whereby an acid solution of a gallium salt is obtained, which also contains minor amounts of sodium and aluminum salts.
In another known process, sodium and aluminum values are stripped in a first stage from the charged organic solution of the extractant by means of a more highly concentrated hydrochloric acid solution, while the gallium values remain in the organic phase in the form of complexes. Following the separation of the acid containing the salt, gallium is stripped in a second stage from the organic phase using a dilute solution of hydrochloric acid. The gallium chloride solution is separated, as an intermediate product, from the organic phase.
Finally, according to a third known process, gallium, sodium and aluminum values are simultaneously stripped in a first stage from the charged organic solution of the extractant, whereby an acid solution containing gallium, sodium and aluminum salts is obtained as an intermediate product.
In all of the known processes, the intermediate product can be purified further in known manner and the gallium values recovered.